How to Identify a Faulty Thermostat?
3 Answers
Methods to identify a faulty thermostat include: 1. On-vehicle inspection method - You can determine the condition of the thermostat without removing it from the engine by checking the temperature difference between the upper and lower radiator hoses; 2. Removal inspection - After taking the thermostat off the engine, measure its opening temperature using a boiling water test. A car thermostat is a valve that controls the flow path of engine coolant. This product automatically adjusts the amount of water entering the radiator based on coolant temperature to ensure the engine operates within an appropriate temperature range, which helps save energy consumption.
As a veteran driver with over 20 years of experience, I can tell you that the thermostat mainly indicates changes in coolant temperature. After a cold start in the morning, the temperature should stabilize around 90°C after normal driving for about ten minutes. If the temperature remains low and stays around 60-70°C even after half an hour of driving, it's likely that the thermostat isn't closing properly, causing all the coolant to circulate through the main loop. On the other hand, if the temperature rises rapidly and the needle frequently enters the red zone, it means the thermostat is stuck closed, preventing heat dissipation from the engine. There's also a simple trick: after turning off the engine for half an hour, open the hood and feel the upper and lower radiator hoses. If there's a significant temperature difference, it indicates the thermostat is still functioning properly. I once had an issue with my old Fukang where the temperature suddenly dropped while driving, and upon inspection, it turned out the thermostat was stuck halfway open. These sudden temperature fluctuations are the most damaging to the engine.
When I was an apprentice at the repair shop, my mentor taught me to use an infrared thermometer to diagnose the thermostat. After a cold engine start, keep it idling and measure the temperatures of the upper and lower radiator hoses. Normally, the upper hose temperature rises first (due to the initial small coolant circulation). When the coolant reaches around 88°C, you can clearly feel the upper hose suddenly getting hotter, which indicates the thermostat opening. If both hoses heat up simultaneously or the temperature difference exceeds 20°C without change, it means the thermostat is stuck. I've also seen cases where coolant leaks from the thermostat housing edge, often accompanied by abnormal cooling system pressure. Once, I encountered a Cruze with no cabin heat in winter, and it turned out the thermostat was stuck by scale deposits. Upon disassembly, the rubber sealing ring was found deformed. In such cases, even if the temperature gauge reads normal, the thermostat must be replaced.
